FRISCO — Studying volcanic vents near the Italian coast has helped scientists gain a glimpse of how increasingly acidic waters could impoverish ecosystems by reducing biodiversity. The study focused in differing levels of acidity around the vents, where carbon dioxide gas bubbles into the water naturally.

“The background, low-grade stress caused by ocean acidification can cause a whole shift in the ecosystem so that everything is dominated by the same plants, which tend to be turf algae,” said lead author Kristy Kroeker, a postdoctoral researcher at the Bodega Marine Laboratory at UC Davis.

“In most ecosystems, there are lots of different colorful patches of plants and animals — of algae, of sponges, of anemones,” Kroeker said. “With ocean acidification, you lose that patchiness. We call it a loss of functional diversity; everything looks the same.”

The researchers selected three reef zones–of low, high and extremely high acidity, representing world ocean conditions for the present day, 2100 and 2500, respectively. Then they removed animals and vegetation from the rocks there. Every few months for three years, Kroeker dived to the study plots to photograph them and watch how the plots in each zone recovered.

By examining how recovery differed among zones, the study found that acidic water reduced the number and variety of species. In the non-acidic plots, many different plants and animals, including turf algae, would colonize and grow. Calcareous species, such as sea urchins and snails, would then eat them, allowing for variety through time.

However, in both the high and extremely high acidic plots, fleshy turf algae increased steadily and overtook the zones, as the urchins and other grazers were either not present or did not graze on the algae while in these zones.

Calcareous grazers play key roles in maintaining the balance within marine ecosystems. They are also considered among the most vulnerable species to ocean acidification.

“Our research is showing that if the role of these grazers changes with ocean acidification, you might expect to see cascading effects of the whole ecosystem,” Kroeker said. “If the pattern holds for other calcareous grazers, this has implications for other ecosystems, as well.”